Photography is all about light, the direction of the light falling on your subject is most important, you must look at your subject carefully and see how the shadows fall.
If you are able to choose the time of day to shoot your pictures, try to pick a time when the sun is low in the sky, either shoot in the early morning or late afternoon. Shooting pictures of people with the sun too high in the sky, tends to mean the subject's eyes will be in shadow and/or your subject will be squinting in the strong light, both of which tend to look horrible. A nice side effect of shooting in the early morning or late afternoon is that the colour of the light is 'warmer', reds and yellows are stronger which generally gives a more pleasing effect.
If you are photographing in sunlight, try to position yourself so that the sun hits your subject from the side, this will give you nice 'modelling' and help create a 3D effect in the picture.Sunlight behind the subject can give a very pleasing 'backlight' effect but be careful that you are not getting 'flare' in the lens, which degrades the contrast of the image.